Electrophotography is a useful process for printing images on a receiver (or “imaging substrate”), such as a piece or sheet of paper or another planar medium, glass, fabric, metal, or other objects as will be described below. In this process, an electrostatic latent image is formed on a photoreceptor by uniformly charging the photoreceptor and then discharging selected areas of the uniform charge to yield an electrostatic charge pattern corresponding to the desired image (a “latent image”).
After the latent image is formed, charged toner particles are brought into the vicinity of the photoreceptor and are attracted to the latent image to develop the latent image into a visible image. Note that the visible image may not be visible to the naked eye depending on the composition of the toner particles (e.g. clear toner).
After the latent image is developed into a visible image on the photoreceptor, a suitable receiver is brought into juxtaposition with the visible image. A suitable electric field is applied to transfer the toner particles of the visible image to the receiver to form the desired print image on the receiver. The imaging process is typically repeated many times with reusable photoreceptors.
The receiver is then removed from its operative association with the photoreceptor and subjected to heat or pressure to permanently fix (“fuse”) the print image to the receiver. Plural print images, e.g. of separations of different colors, are overlaid on one receiver before fusing to form a multi-color print image on the receiver.
Electrophotographic (EP) printers typically transport the receiver past the photoreceptor to form the print image. The direction of travel of the receiver is referred to as the slow-scan, process, or in-track direction. The direction perpendicular to the slow-scan direction is referred to as the fast-scan, cross-process, or cross-track direction. “Scan” does not imply that any components are moving or scanning across the receiver; the terminology is conventional in the art.
Various undesirable toner features (artifacts) can appear on prints produced by electrophotography. One type is a comet, which is a light splotch of toner (or, more generally, an area of increased density) spanning a restricted extent of the cross-track direction.
U.S. Pat. No. 5,532,795 to Tatsumi et al. describes cleaning rollers in a printer. GB2282781 describes cleaning elements urged into contact with the surface of a charging roller. However, these schemes can cause damage to the rollers, and are not applicable to stationary surfaces such as skive mounts.
U.S. Pat. No. 7,555,236 describes cleaning a transfer drum electrostatically. Electrical bias is modified to clean. U.S. Pat. No. 5,552,795 describes engaging a secondary drum and modifying electrical signals to attract toner to a waste area. This is used to clean a transfer drum of developer or toner that has not transferred to a photoreceptor. However, the toner or developer deposited on a skive mount does not have a controlled charge, so electrostatic methods are not capable of reliably cleaning the skive mount.
U.S. Pat. No. 7,627,280 describes tubes for carrying waste through a printer. The waste is the developer which has escaped the normal development cycle and is transported to a removal container. However, this scheme is not useful for removing toner from a skive mount.
Skive mounts adjacent to development rollers can collect stray toner during operation. When the toner layer on the skive mount becomes thick enough, toner can fall off onto the development roller, causing a “comet” artifact, an area of increased density in the print. There is a need, therefore, for a system for correcting these defects.